The present invention relates to an amplifier having an amplifier input, the amplifier comprising: xe2x80x94a first controllable semiconductor having a first controllable mainstream path coupled to first source means for controlling the first mainstream path, and having a first biased control input; and xe2x80x94a second controllable semiconductor having a second controllable mainstream path coupled to second source means for controlling the second mainstream path, and having a second control input coupled to the first main stream path and to the amplifier input.
The present invention also relates to a communication device provided with an antenna amplifier, optical amplifier, low noise amplifier, RF mixer, hard-disk drive read amplifier, GSM or DECT device, and the like, which communication device is provided with such an amplifier.
Such an amplifier is known from WO 96/11528. The amplifier arrangement known therefrom comprises a first transistor as a controllable semiconductor having a first collector emitter mainstream path coupled to a first current source for controlling the first mainstream path, and a having first biased control input; and comprises a second transistor having a second collector emitter mainstream path coupled to a second current source for controlling the second mainstream path, and having a second control input coupled to the first main stream path and to the amplifier input. In an embodiment the first transistor is anti-parallel connected to a further transistor between two outputs of the amplifier. In series with the second transistor there is a still further transistor taking over the control from the second transistor in case of a large signal excursion due to a large amplifier input signal. Thus it is ensured that all transistors remain biased irrespective actual input signal excursions, which reduces signal distortion of the amplifier.
It is a disadvantage of the known amplifier that matching of an input signal source, which provides the input signal and an input section of the amplifier concerned is not optimal, as a consequence of which input impedance and input noise characteristics respectively each lack appropriate matching, which degrades performance characteristics of the amplifier and/or corresponding communication device provided therewith.
Therefore it is an object of the present invention to provide an amplifier and communication device, whose input impedance and input noise characteristics are both optimally matched to the characteristics of the input signal source of the amplifier.
Thereto the amplifier and communication device according to the invention are characterised in that both the first and second mainstream paths are coupled to a common load, and that the first and second source means are arranged for controlling input impedance and noise impedance respectively of the amplifier input.
It is an advantage of the amplifier according to the present invention that it has been found that by independent control of each of the individual first and second source means a virtually independent input impedance and noise impedance control can respectively be achieved. Consequently optimisations of both input impedance and noise impedance can be reached separately. Because power matching is related to impedance matching, the former matching is also possible. Even dynamic and adaptive matching of each of these impedances is feasible in a simple way, without any operational stability problems raising feedback structures being necessary therefor.
An embodiment of the amplifier according to the invention is characterised the amplifier is an RF amplifier.
Advantageously even broadband RF input impedance matching is possible, such that the amplifier gain is more constant over a larger frequency band, whereby antenna sizes may be decreased, because in particular low noise operation at lower impedances requires smaller antennas. These smaller antennas can thus be integrated more easily on chip or in a casing of mobile or portable telephones.
A further alternative and easy to implement embodiment of the amplifier according to the invention is characterised in that the amplifier comprises a third controllable semiconductor, whose third mainstream path is connected in series with the second mainstream path of the second controllable semiconductor, and having a third control input which is coupled to the first biased control input.
Generally the controllable semiconductors are transistors, in particular embodied by MOS, such as P-MOS or N-MOS, or bipolar NPN or PNP transistors, which are widely available and easy to integrate on only a limited IC chip area.
In a differential configuration of a communication device it may be preferred to have an amplifier according to the invention be characterised in that the amplifier is embodied as a differential amplifier.